Vacuum tube having thyratron characteristics



March 7, 1961 A. M. SKELLETT VACUUM TUBE HAVING THYRATRON CHARACTERISTICS Filed July 13, 1959 INVENTOR. M. SKELLETT ALBERT FIG. 3.

5 m, 4w1w. Mica):

A T TORNE Y5.

United States VACUUM TUBE HAVING THYRATRON CHARACTERISTICS Albert M. Skellett, Madison, NJ., assignor to Tung-Sol Electric Inc., a corporation of Delaware Filed July 13, 1959, Ser. No. 826,518

'8 Claims. (Cl. 313-71) conduct regardless of the condition of the initiating control unit.

Thyratrons' having either hot or cold cathodes with,v firing grids and various types of gas fillings have been well known for some time and have been very useful in the electronic industry. An important characteristic of the thyratron is its ability to support conduction between its anode and cathode after having been fired by the con-' trol electrode. After conduction has been started the thyratron can be changed to a non-conducting condition only by reducing the anode voltage to zero. When the conduction between anode and cathode is stopped the anode voltage can not again be applied until after a certain time interval known as the deionization time. Some selected gases at certain pressures have a very short deionization time but this feature of the thyratron tubes is a distinct disadvantage when working withhigh. frequencies.

The present invention comprises a vacuum tube without. any appreciable gas within its envelope and for this reason the gas deionization time is zero. After conduction has been cut off between the anode and its adjacent cold cathode the voltage may be applied immediately without. starting anode-cathode conduction. This feature and; other advantages to be described later make the discharge device a useful electronic component with a combination of'features exhibited by no other electronic tube. I

One of the objects of this invention is to provide an proved electron discharge device which avoids one or; more of the disadvantages and limitations of prior art; arrangements. l

1' Another object of the invention is to provide avacuum= discharge device having most of the characteristics ofaj, thyraton gaseous discharge deviceJ 7 Another object of the invention. is to provide a cold cathode, discharge device which has low internal resistance and high efliciency 1 Another object of the invention is to provide a dis-j. charge device having most of the characteristics of" a; gaseous thyratron without the disadvantages encountered because of gas clean up, gas impurities, change in pressure dueto temperature effects, and many other disadvantages generally associated with gas-filled tubes.

The new vacuum tube includes a diode comprising a cold cathode with a magnesium oxide coating and anflad jacent anode with apertures-for theapplication'jof elec trons from an outside source. In the same envelope a hot cathode is mounted surrounded by a control grid and a screen grid. In order to direct electrons from the hot cathode to the cold cathode an electrostatic shield is used. This shield generally surrounds the hot cathode elements and is maintained at a zero or a negative potential with respect to the hot cathode.

streams from the hot cathode. anode 19 comprises a plurality of vertical rods connected together at their ends'but spaced apart from each other For abetter understandingv of the present invention,

together with other and further objects thereof, reference is made to the following description taken in connection withthe accompanying drawing. Q

. Fig. 1 is aside view of the vacuum discharge device with some parts in section. 7

' Fig. 2 is'a cross sectional view of the tube shown in Fig. l andis taken along line 22 of that figure.

Fig. an a cross sectional view similar to Fig. 2 but showing an alternate arrangement of components.

Referring now to the drawing, the discharge device includes an envelope 10 which encloses a hot cathode 11 surrounded by a control grid 12 and a screen grid 13. The hot cathode may be fabricated in the usual manner and includes a heater and a hollow metallic support for emitter material. The control grid 12 is preferably ma'cle of a wire mesh or the usual parallel wire construction and is connected to an external source of potential which may be varied between a negative cut-off potential of about 10 volts to zero potential when the diode elements are to be made conductive. The screen grid has the same general structure as the control grid and is maintained at a positive potential with respect to the cathode 11 of about to 250 volts. The screen grid is designed to give the electron beams a medium velocity for traveling toward the cold cathode.

Surrounding most of the hot cathode structure is an electrostatic shield 14 which is maintained at zero potential with respect to the hot cathode. This shield serves to deflect and redirect the electronbearns as they are emitted from the hot cathode.

The diode portion of the vacuum tube includes a hollow cylindrical coldcathode 15 as shown in Fig. 2. The same cathode is shown in Fig. 3 as a plane metal surface 16 having cooling fins 17 on one side. The cold cathode surface is coated with a porous coating of magnesium. oxide and may be maintained at apotential of 200 volts positive with respect to'the hot cathode 11. Surrounding the cathode, as shown in Fig. 2', is a cylindrical anode 18.

having a plurality of apertures for the passage of electron As shown in Fig. 3 the for-the passage of electrons. In order to shield the, cold cathode coating, a mask 20 is placed adjacent to one pm- 7 tion of the screen grid, This mask protects the mag nesium oxide from molecular impurities given off by the It is normally connected to the hot cathode. When the tube is operated, the following voltages are 0 applied to the electrodes:

Hot cathode 11 0 volts"ground.

hot cathode.

Control grid 12 .10 volts.

Screen grid 13 200 volts. Electrostatic shield 14 -Q 0 volts-ground. Cold cathode 15, 16 .200 volts. Anode 1s, 19. 400m 600.volts.

With the above potentials, no conduction results because the negative potential of the control grid prevents to about zero and a supply of electrons is projected through the two grids to the space within the shield-14. 1 I The electronshave considerable speed because of the high voltage on the .screen grid, and they are deflected bylth'e" electrostatic field between the shield and the other electrodes and are directed toward the cold cathode which drawn toward the anode 18 of Fig. 2 or 19 of Fig. 3. The emission from the magnesium oxide coating is thereby started and such emission continues as long as the anode is maintained at a voltage of at least 180 volts above that of the cold cathode. The anode-cathode current is maintained between the cold cathode and anode aslong as the potential difference between them is suflicient to cause electron emission regardless of the action of the hot cathode source 11, 12, 13. It is even possible to turn off the heater current and disconnect all voltage sources to the cathode 11, grids 12 and 13 and to the shield 14.

When the potential difierence between anode 18 or 19 and the respective cold cathode 15 or 16 is reduced to a low value or Zero, the current between them immediately stops, irrespective of the voltages applied to the hot cathode and grids 12 and 13. After thepotential difference is restored conduction is again under control of the control grid 12 which controls the electron streams from the hot cathode. Thus the new tube, like a gas thyratron tube, is triggered by application ofvoltage to the control grid 12, assuming the anode voltage is sufliciently above that of the cold cathode, and is quenched by reduction of anode potential, the control grid losing control once conduction is started and anode voltage is maintained. Unlike a gas thyratron, no delay in quenching is introduced by deionization time.

It will be obvious from the above description that the electrons from the hot cathode serve onlyto start the emission from the cold cathode and serve no other useful purpose. It has been found by experiment that very high speed starting of the cold cathode emission can be accomplished by this means. If the electron bombardment of the magnesium oxide coating has sutficient energy, starting times of the order of one microsecond or less are possible.

In the foregoing example, a hollow heated cathode was described within control grid 12. A filamentary cathode of tungsten can be used with the same results.

The tube shown in Fig. 3 is the same as Fig. 2 except that the cathode emitting surface 16 is plane and its support is provided with heat radiators 17. The anode 19 is disposed in parallel relationship and contains holes or channels for the passage of electron streams from cathode 11.

The characteristics of the diode 15, 18 of Fig. 2 and the diode 16, 19 of Fig. 3 have been disclosed in US. patent applications filed February 25, 1959, Serial No. 795,514 and April 24, 1959, Serial No. 808,618, both by Bernard G. Firth.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

I claim:

1. An electron discharge device comprising: a sealed envelope enclosing a cold cathode having a coating of porous magnesium oxide, an anode adjacent to the cold cathode and having holes for the passage of electrons, a source of electrons which includes a hot cathode, a control electrode, and a screen grid, and an electrostatic shield surrounding said electron source, said shield designed to change the directions of electrons emitted by the hot cathode source to direct them toward the cold cathode.

2. An electron discharge device comprising: a sealed envelope enclosing a thermionic cathode with a control electrode for controlling the flow of electrons therefrom, a cold cathode having a coating of magnesium oxide, an adjacent anode containing holes for the passage of electrons, and means for directing a primary stream of electrons from the thermionic cathode through the anode holes to the cold cathode.

3. An electron discharge device comprising: a sealed envelope enclosing a thermionic cathode with a control electrode for controlling the flow of electrons therefrom, a cold cathode having a coating of magnesium oxide, an adjacent anode containing holes for the passage of electrons, and a curved electrode with its concave surface facing both cathodes for constraining the electrons emitted by the thermionic cathode to follow a curved path toward the cold cathode.

4. An electron discharge device comprising: a sealed envelope enclosing a thermionic cathode with a control electrode for controlling the flow of electrons therefrom, a cold cathode having a coating of magnesium oxide, an adjacent anode containing holes for the passage of electrons, means for directing a primary stream of electrons from the thermionic cathode to the cold cathode, and a solid shield mounted between said thermionic cathode and said cold cathode and extending across any straight line between any point of the thermionic cathode and the cold cathode.

5. An electron discharge device comprising: a sealed envelope enclosing a thermionic cathode having an adjacent control electrode and a screen grid, a cold cathode spaced apart from the thermionic cathode and having a coating of porous magnesium oxide, an anode mounted in parallel relationship to said cold cathode and containing holes for the passage of electrons from the thermionic cathode, a curved electrode with its concave surface facing both cathodes for constraining the electrons emitted by the thermionic cathode to follow a curved path toward the cold cathode, and a solid shield mounted between the thermionic cathode and the cold cathode and extending across any straight line between any point of the thermionic cathode and the cold cathode.

6. An electron discharge device comprising: an evacuated envelope enclosing a cold cathode having a porous coatingthereon of the type adapted to emit a stream of electrons once emission is initiated, which emission becomes self-sustaining provided there is present an electrode of sufiiciently higher potential for collection of the emitted electrons, an apertured anode adjacent said cold cathode to serve as a collector electrode for electrons emitted by said coating, a source of thermally generated electrons, at least one grid for controlling electrons from said source and an electrostatic shield for directing electrons from said source through the apertures in said anode toward said cathode to initiate electron emission therefrom, whereby conduction between said cathode and anode may be triggered by control potentials applied to said grid and quenched by reduction of potential of said anode.

7. The electron discharge device according to claim 6 including a solid shield mounted between said source and said cathode and extending across any straight line between any point of the source and the cathode.

8. The device according to claim 6 wherein said source of thermally generated electrons is a heated cathode, said grid is a control grid encompassing said heated cathode and wherein an electron accelerating grid encompasses said control grid.

References Cited in the file of this patent UNITED STATES PATENTS 

